The U.S. economy returned to its sluggish trajectory late last year, though underlying signs of strength suggest growth will pick up in 2015. Gross domestic product, the broadest measure of goods and services produced across the economy, expanded at a 2.2% annual rate in the fourth quarter, the Commerce Department said Friday, weaker than an earlier 2.6% estimate.The latest figures show the 5% pace in the third quarter and 4.6% in the second quarter were unsustainable. For 2014 as a whole, GDP expanded 2.4%, slightly better than the average 2.2% growth of 2010-13. By comparison, the economy grew an average 3.4% a year during the 1990s. Still, Friday‚Äôs report showed that consumer spending, which accounts for about two-thirds of output in the U.S., matched its fastest pace since early 2006 during the fourth quarter. Personal consumption expenditures advanced 4.2%. Consumers have been the brightest spot in recent months. […]